In moderate force, the soleus is
preferentially activated in the concentric
phase, whereas the gastrocnemius is preferentially activated
in the eccentric
phase. The gastrocnemius becomes even more activated at higher
lengthening velocities (Nardone & Schiepatti, 1988). During
hopping, the gastrocnemius, with its greater proportion of fast
twitch motor units, is preferentially activated over the soleus
(Moritani et al., 1990). During stationary cycling, the gastrocnemius
is also preferentially activated at higher pedaling speeds (Duchateau
et al., 1986).

Although the involvement of the lateral and medial heads would
not seem to be altered by medial
or lateral rotation
of the hip, magnetic resonance imaging (MRI) research by
Dr. Per Tesch (Sweden) suggests "toes in" activate
both heads and "toes out" activate the medial head
to a higher degree. See dorsiflexion
inflexibility.